1. Field of the Invention
The invention relates to a device for exposure of a strip-shaped workpiece with a meander correction device, in which image processing determines the edge length information of the strip-shaped workpiece in the transverse direction and based on the obtained position information, the meander of the strip-shaped workpiece which occurs during transport is corrected.
2. Description of the Related Art
It is known that in a device for exposure of a strip-shaped workpiece (hereinafter also called a “workpiece”), a mask and the workpiece are aligned with one before exposure using alignment marks. These marks can be formed in the workpiece when a pattern which has been formed in the mask, such as a circuit or the like, is exposed onto the workpiece.
However, if a first exposure is carried out on the workpiece and neither the pattern, such as a circuit or the like, nor workpiece marks are formed, the above described positioning cannot be performed.
In the first exposure, the accuracy of the distance between the patterns to be exposed is determined by the positioning accuracy in the transport direction and depends on the transport accuracy with which the device transports the workpiece.
Furthermore, the distance in the transverse direction between the pattern and the workpiece edge is fixed. But if a meander forms during the transport of the workpiece, the position of the pattern to be formed deviates in the transverse direction or becomes slanted. Therefore, the meander of the workpiece must be corrected.
One technique which relates to meander correction of a strip-shaped workpiece is described in Japanese patent JP 9070731.
In the first embodiment in the aforementioned Japanese patent, two optical sensors formed of a light receiving component with a relatively large light receiving surface and an emission element are located upstream and downstream of a strip-shaped workpiece. This arrangement allows for a determination of a meander of the strip-shaped workpiece. Correction of the meander is done by holding the edge area of the strip-shaped workpiece with two clamps and stretching or pressing the workpiece in the transverse direction.
If the amount of light received by the light receiving component of the two optical sensors is within a predetermined meander tolerance range, it is assessed that there is no meander. When the amount of light received by the light receiving component of the two optical sensors is outside the predetermined meander tolerance range, the above described holding parts are moved by a distance which corresponds to the difference of the amount of light received, and thus the meander is corrected.
In a second embodiment of the aforementioned Japanese patent, there are two optical sensors upstream and two optical sensors downstream of the strip-shaped workpiece. Each optical sensor consists of a light receiving component with a relatively small light receiving surface and an emission element. The state in which the two light receiving components located on the inside are shielded and the two light receiving components located on the outside receive the light from the emission components is assessed as “meander not present”. All other cases are assessed as “meander present”. In cases of “meander present”, the holding parts are moved and the meander is corrected in the above described manner.
In the first embodiment in the aforementioned Japanese patent, optical sensors with a relatively large light receiving surface are used. These optical sensors can be large and costly.
In the second embodiment in the aforementioned Japanese patent, the allowable meander area is fixed by the amount of light of the optical sensors or by the positions of the optical sensors, which are each located in two pieces. Fixing the tolerance of the meander of the workpiece is however difficult. This is especially true in the case of fixing the tolerance of the meander by the change in the amount of light of the optical sensors as disclosed in the first embodiment of the aforementioned Japanese patent. With respect to the adjusted threshold value of the amount of light in the first embodiment, sensors are needed which output signals with high precision and good reproducibility. There are many cases in which these sensors require a light source from which parallel laser light emerges, and are therefore very costly and large.
Furthermore, in the second embodiment of the aforementioned Japanese patent in which the allowable meander area is fixed by the positions of the optical sensors which are each located in two pieces, the sensor number is large, resulting in relatively high costs. Furthermore, it is difficult to install the sensors exactly at the fixed locations. They are installed mechanically, resulting in major errors as well.
In the above described Japanese patent, the strip-shaped workpiece is held by the clamps and thus meander correction is done. If the strip-shaped workpiece is relatively thin, the meander correction may fail because the clamps may be unable to hold the workpiece. Furthermore, depending on the types of workpieces, there are cases in which static electricity causes the workpiece carrier and the strip-shaped workpiece to stick to one another and therefore prevents movement of the workpiece. If the workpiece is relatively thin and soft, there are cases in which the clamps deform the workpiece, thereby preventing meander correction.